The present invention relates to the dry end or dryer section of a machine for the manufacture of a fibrous web, particularly a web of paper. In particular, the invention concerns a dry end of the type which is formed exclusively of so-called single-screen dryer groups. Dry ends of this type are known from the following publications.
1. Journal "Wochenblatt fur Papierfabrikation", No. 22, 1988, page 6.
2. WO 90/01580, corresponding to U.S. application Ser. No. 230,627, filed Aug. 10, 1988.
3. WO 90/02225, corresponding to U.S. application Ser. No. 235,394, filed Aug. 23, 1988.
These publications disclose that the dryer cylinders can be arranged either in at least approximately horizontal rows or in at least approximately vertical rows at least over the greater part of the dry end. It is further known that to subdivide such a dry end into several dryer groups, wherein each dryer group comprises a plurality of heatable dryer cylinders, a plurality of guide rolls and a support belt which presses the web which is to be dried against the dryer cylinders.
From above Publication 1., it is known to provide single-screen dryer groups exclusively between the press section and the calender of the paper machine. However, there are also paper machines in which a dry end consisting exclusively of single-screen dryer groups extends from the press section up to a size press or a similar intermediate station, or from a size press to a calender.
It is further known from such publications that the bottom side of the web always comes into contact with the dryer cylinders in the last dryer group. In this way, the web travels in the downward direction, in particular, from the last dryer cylinder in the downward direction. In this way, in case of any disturbance, the web can be easily removed in the downward direction into a broke pulper.
From above Publications 2. and 3., it is known that a tip cutter must be installed at the end of the dry end. As long as the web travels into the broke pulper, the tip cutter can cut a narrow edge strip from the web. This strip then serves for threading the web into the following treatment stations, for instance calender and reel, or size press, or the like. A free stretch or draw of web is formed for such a tip cutter by means of a special arrangement of rollers, since upon the cutting of the tip, the web must be free of the support belt which otherwise travels with the web.
In Publication 2., the free stretch or draw of web is formed at the place of separation between the next-to-the-last and the last dryer groups, and therefore at a place where the web is still not completely dry. Thus, there is a danger that the web will tear upon the cutting of the tip. On the other hand, if necessary, use can be made of the possibility of controlling the web tension upon the cutting of the tip, by changing the difference in speed between the two dryer groups.
In Publication 3., the free stretch or draw of the web is formed within the last group of dryers, preferably between the last two dryer cylinders, and therefore at a place where the web is completely dry. Thus, the web only rarely tears upon the cutting of the tip. Between the last two dryer cylinders, there is a reversing roll with which the support belt comes into direct contact. In addition, a web guide roll is arranged below this reversing roll. The web travels, free of the support belt, from the reversing roll to the web guide roll and from the guide roll back to the reversing roll so that two free stretches of web are present. The aforementioned tip cutter is arranged on one of these two free stretches or draws of web. With this arrangement, there is the danger that upon tearing of the web or upon some other unstable operating condition, the web will wind up on the web guide roll. Furthermore, this has the disadvantage that two free stretches of web are present, although only a single free stretch of web is necessary for the tip cutter. The danger of tearing, which is always present at each free stretch of web, is therefore unnecessarily increased.